The maintenance of solenoid-controlled injectors fitted to internal combustion engines is an operation commonly performed in garages and on other vehicle maintenance premises. This operation may be regular or occasional because malfunctioning is suspected or proven and because a diagnosis is necessary prior to any repair. The maintenance operation requires checking of the electrical characteristics of the solenoid such as the measurement of resistance, measurement of the insulation value and measurement of inductance. Furthermore, a control test, also called an actuator test or buzz test, is sometimes possible. During this test the injector is activated and then emits an audible buzz.
At present an operator in charge of maintenance performs the electrical measurements by means of a standard multimeter, varying the points of taking measurements according to the characteristic observed. Some solenoids have low resistance, and the standard multimeter is not precise enough to give an exact value, special multimeters must be used. The same applies to the measurement of inductance.
Furthermore, the buzz test can be performed only if the electronic control unit for the injector is provided with such a function, then implemented via a specific tool. Few control units are provided with this function. The buzz test in itself also has certain limits. When the operator launches the buzz test and no buzz is audible, this does not necessarily mean a fault at the level of the solenoid. The operator must still identify which element of the control circuit is at fault. He generally begins with the insulation and the electrical continuity of the wiring harness, then continues with the electrical measurements of the solenoid itself, then, if no fault has been detected, the operator replaces the injector with a new injector. Lastly, if nothing is detected during these steps, the operator replaces the control unit after the customary checks: condition of fuses, earths correctly connected, electrical contacts clean, etc. The checking of electrical continuity of the wiring harness is, in itself, an operation which may prove to be lengthy, depending on whether the electrical architecture of the vehicle is simple or more complex, and this check may require the use of a specific junction box.
Furthermore, in the event that a buzz is audible during the buzz test, the operator cannot directly conclude that the injector is functioning properly either. For example, if the electrical resistance measured is too high, the injector may nevertheless be actuated and controlled owing to an electrical current which is just high enough, but still not sufficient to allow precise control of injection. There too, identification of the fault involves measurements of low resistance, lower than 1 Ω, and very difficult to measure with a standard multimeter such as those commonly used in maintenance workshops and capable of measuring a much greater electrical resistance, a DC or AC voltage and an electrical current.
With the aim of saving time devoted to any necessary investigation, the operator frequently proceeds directly to changing the injector without making a particular diagnosis. In numerous cases this operation eliminates the symptom, but without getting rid of the actual cause, and then the problem reappears after some time. This is typically the case when poor contact or ageing of the circuit gives rise to a slight increase in resistance of the circuit, which is then simply higher than a maximum expected value. A new injector, having a relatively low electrical resistance of its own, will decrease the total resistance to below the expected limit, but without providing a solution to the problem of contact or ageing, and the fault will not fail to reappear.
Among other problems encountered during the normal life of a vehicle, some injectors become partially obstructed by lacquering or by deposition of residue. At present there are no means which allow lacquered injectors to be cleaned easily.
It therefore appears that a significant demand by the market, and particularly vehicle maintenance professionals, is to have a reliable and easy-to-use means allowing the necessary checks to be carried out with precision as well as cleaning operations. The ideal being to be able to carry out all measurements and operations without dismounting the injector from the engine. Moreover, the professionals see to the upkeep of injectors of different types, and it would be inconceivable to duplicate the maintenance tools each time a new injector is put on the market. A single and adaptable system is therefore necessary.